Biological optical measuring instrument

ABSTRACT

A biomedical optical measurement apparatus comprising a light source unit for generating an inspection light containing multiple lights modulated at different frequencies, a light-receiving unit for receiving the light generated at said light source unit and passing through an object to be examined and for outputting the electric signals with the intensity corresponding to the received inspection light, and a detection means for detecting a signal with the same frequency of the reference signal in the output from said light-receiving unit. The detection means comprises an analog-digital conversion means for outputting digitized data by converting an input signal to a digital signal, a storage means for storing digitized data of multiple reference signals, a digital multiplication means for multiplying digitized data of input signals outputted from the analog-digital converting means by the digitized data of the reference signals read out from the storage means and for outputting the product of multiplication, and a digital band-limitation means for taking out DC data from the output from the digital multiplication means. Reference signal generating circuits of a number equal to that of frequencies of detected signals, which has been necessary for the conventional instrument, can be replaced by a single memory means and the configuration of the instrument can be simplified. Changes in frequency can be easily coped with by only re-writing the data of the storing means.

CROSS REFERENCE TO RELATED APPLICATION

This Application is a U.S. National Stage Application filed under 35U.S.C. § 371 of PCT/JP02/07350 Jul. 19, 2000.

FIELD OF INVENTION

The present invention relates to a biomedical optical measurementapparatus, which measures inside the living body by receiving a lightthat has passed through the living body. Particularly, the inventionrelates to the biomedical optical measurement apparatus equipped with animproved detection circuit, which can distinguish and detect a light tobe detected at multiple light-receiving positions.

Prior Art

The field of clinical medicine and brain science are strongly expectingto have a measuring instrument, which allows easy measurement inside theliving body without giving hazardous damage to a living body. To meetsuch expectation, biomedical optical measurement apparatuses formeasuring inside the living body by receiving a light passing throughthe living body, such as those disclosed and claimed in the JapanesePatent Application Laid-Open Nos. 9-149903 and 2000-300569 have beenproposed. These biomedical optical measurement apparatuses described insuch patent publications have a configuration in which an inspectionlight composed of multiple lights modulated at different frequencies isirradiated onto the multiple positions of an object to be examined, onlythe light passing through the object is received and signals withspecific frequencies are detected from electric signals with theintensity corresponding to the passed light using a lock-in amplifier(biomedical) to obtain information on the living body, particularly onthe blood circulation, in the area including multiple irradiationpositions.

There is also a biomedical optical measurement apparatus, which isequipped with a time-sharing light irradiating and receiving means inorder to obtain information from multiple irradiation positions. Thisbiomedical optical measurement apparatus does not use an aforementionedlock-in amplifier but has a configuration wherein the light isirradiated sequentially from the light source unit (light emittingprobe) and received sequentially at the light-receiving unit(light-receiving probe) with both irradiation and receiving of lightbeing controlled by clock signals, thereby identifying measurementposition.

Configuration and problems of the detection circuit used in theseconventional biomedical optical measurement apparatuses are explainedbelow.

FIG. 14 shows a block diagram showing a schematic configuration of alock-in amplifier employed in the conventional biomedical opticalmeasurement apparatuses. The light-receiving element 171 receives aninspection light that passed through an object to be examined, performsphotoelectric conversion and outputs electric signals with the intensitycorresponding to the light to the amplifier 172. The signal amplified bythe amplifier 172 is inputted as an input signal 173 in each lock-inamplifier. The input signal 173 is a synthesized signal made of multiplesignals with different frequencies. Reference signal generating circuits1751 to 175 n output reference signals having the same frequencies asthose of signals to be detected in the multipliers 1741 to 174 n,respectively. The multipliers 1741-174 n multiply individual inputsignal 173 by the reference signal from the reference signal generatingcircuits 1751 to 175 n and output the products in the low-pass filters1761 to 176 n. The low-pass filters 1761 to 176 n take out the directcurrent component from the output at multipliers 1741 to 174 n andoutput them as output signals 1771 to 177 n. The multipliers 1741 to 174n, the reference signal generating circuits 1751 to 175 n and thelow-pass filters 1761 to 176 n are provided in the number of frequenciesto be detected (n). The outputs from the low-pass filters 1761 to 176 nare introduced through the A/D converter, which is not shown in thefigure, into the processing circuit of PC and undergo signal processing.

FIG. 15 shows a block diagram showing a detailed configuration of one ofthe multiple lock-in amplifiers shown in FIG. 14. Since each lock-inamplifier has the same configuration, except frequency of a referencesignal to be used, the lock-in amplifier shown at the top of FIG. 14 isexplained. This lock-in amplifier is configured to detect a directcurrent component of the input signal having the same frequency as thatof reference signal by amplifying the output from the amplifier 172,which inputs signals from the light-receiving element 171, by dividingit into two amplifiers 183 and 184, in which positive/negative switchingis performed, and then by outputting the outputs from said amplifiers183 and 184 after switching at the switching circuit 185, which switchespolarity according to the frequency of the reference signals.Specifically, the signal amplified by the amplifier 172 (a synthesizedsignal made of multiple signals with different frequencies) is outputtedas divided into the amplifier 183 and 184. The amplifier 183 amplifiesthe input signal as it is, that is, after multiplying by +1, and outputit at the first terminal of the switch circuit 185. The amplifier 184reverses the polarity of input signal, or multiple by −1, and output itat the second terminal of the amplifier 184. The switch circuit 185supplies output from the amplifier 183 or 184 to amplifier 186 byalternately switching between first and second terminal in accordancewith the reference signal F1 outputted from the reference signalgenerating circuit 1751. Here, the reference signal F1 is a signal whosefrequency is the same as that of the signal to be detected at thislock-in amplifier 185. The amplifier 186 amplifies the signal outputtedfrom the switch circuit 185 and outputs it to the low-pass filter 1761.

FIG. 16 shows a timing chart of signal waveforms, which describes theaction of the lock-in amplifier shown in FIG. 15. FIG. 16(A) shows acase in which the signals to be detected are locked-in by the lock-inamplifier, while FIG. 16(B) shows the case in which other signals thanthose to be detected are not locked in. The signal to be detected is asignal whose frequency is same as that of the reference signal Fn inFIG. 16(A). The input signals contain the signal whose frequency is sameas that of reference signal Fn. When the signal AMP1 (I) outputted fromthe amplifier 172 has the same frequency as the reference signal Fn, thesignal AMP1 (P) outputted from the amplifier 183 is the same with thesignal AMP1 (I), while the signal AMP1 (N) outputted from the amplifier184 is an inverted signal of AMP1 (I). When these signals AMP1 (P) andAMP1 (N) are outputted from the amplifiers 183 and 184, the switchcircuit 185 is switched by the reference signal Fn, thereby outputting asignal AMP1 (O) from the amplifier 186. The direct current component ofthis signal AMP1 (O) passes through the low-pass filter 176 (1761-176 n)and is outputted as a detection signal LPF1.

As shown in FIG. 16(B), if the signal AMP2 (I) outputted from theamplifier 172 has a different frequency from that of the referencesignal Fn, a signal AMP2 (O) is outputted from the amplifier 186.Although a direct current component of this signal AMP2 (O) passesthrough the low-pass filter 176 and is outputted as a detection signalLPF2, the direct current component is zero because its frequency isdifferent from that of reference signal Fn. The lock-in amplifier will,thus, detect only a signal with a particular frequency.

As mentioned above, the lock-in amplifiers used in the conventionalbiomedical optical measurement apparatuses required multipliers,reference signal generating circuits and low-pass filters in the numbersequal to the number of frequencies of signals to be detected. If thefrequency of the signal to be detected is changed, therefore, adifferent reference signal generating circuit had to be provided.

Moreover, if the signal to be detected has a phase difference from thereference signal Fn and/or if the phase difference varies in the lock-inamplifier of the biomedical optical measurement apparatus as shown inFIG. 15, there occurs a problem that the detection signal to beoutputted from the low-pass filter 176 attenuates more than usual andleads to a deteriorated S/N ratio.

FIG. 17 shows a timing chart of signal waveforms, which explains theaction of the lock-in amplifier shown in FIG. 15 when the signal to bedetected has a phase difference from that of the reference signal andthe phase difference varies. FIG. 17(A) shows the case, in which thesignal to be detected have a phase difference from the reference signal,while FIG. 17(B) shows the case, in which the phase difference of thesignal to be detected varies for the reference signal.

As shown in FIG. 17(A), if the phase of signal AMP3 (P) outputted fromthe amplifier 183 is delayed from that of reference signal Fn, such asignal as AMP3 (O) is output from the amplifier 186, and thereby a lowlevel detection signal LPF3 with a small S/N ratio is output from thelow-pass filter 176. Similarly, as shown in FIG. 17(B), when the phaseof the signal AMP4(O) outputted from the amplifier 183 changes diverselyfor the reference signal Fn, the amplifier 186 may output a signal suchas AMP4(O). It is not favorable because the low-pass filter 176 outputsa detection signal LPF4, whose level changes in accordance with thephase changes and whose S/N ratio is unstable.

FIG. 18(A) shows a schematic configuration of a biomedical opticalmeasurement apparatus equipped with a time-sharing irradiating- andlight-receiving means. This biomedical optical measurement apparatus isconfigured, as the biomedical optical measurement apparatus in FIG. 14,to receive an inspection light passing through an object to be examinedat a light-receiving element 161, to convert the light to an electricalsignal (photoelectric conversion), output the signal corresponding tothe intensity of light into the amplifier 162 and input the signalsamplified by the amplifier 16 into the A/D converter 163.

However, this biomedical optical measurement apparatus is equipped witha clock (timing signal) for sequentially processing signals to beoutputted from the light-receiving element in a time-sharing manner.This clock is outputted from the control unit, which is not illustrated,and controls the timing of irradiating a light from the light sourceunit as well as the sampling timing in the A/D converter 163. That is,the A/D converter 163 performs analog-digital conversion at a timesynchronized with the clock signal CLOCK and outputs them in thearithmetic operation unit (PC) 169.

FIG. 18(B) shows a timing chart of an exemplary action. In FIG. 18(B),signals S1 to S5, whose irradiation timing from each light source isshown, are outputted in a desired time-sharing timing by each lightsource. These signals S1 to S5 are outputted as a synthesized signal Dfrom the amplifier 162 into the A/D converter 163. The A/D converter 163converts the signal from analog to digital signal with the timing ofclock signal CLOCK and outputs the digital signal as a detection signal.

In biomedical optical measurement apparatuses, signals detected in thelight-receiving unit are ones passed through an object to be examinedamong incident lights from the light source unit, and the level of lightintensity is extremely low. FIG. 19 shows a biomedical opticalmeasurement apparatus, which is modified by improving the biomedicaloptical measurement apparatus FIG. 18(A) so as to increase an S/N ratioof the signal detected in the light-receiving unit. The biomedicaloptical measurement apparatus shown in FIG. 19 is equipped with anintegrator 170 prior to the AD converter 163. The integrator 170 isreset at a time synchronized with the clock signal CLOCK, while the A/Dconverter 163 performs A/D conversion at a time synchronized with theclock signal CLOCK. By installing this integrator 170, the level of thedetection signal IntD at the time of analog-digital conversion by theA/D converter becomes higher than that of the signal D as shown in FIG.19(B), thereby leading to the sufficiently large S/N ratio.

In the biomedical optical measurement apparatus equipped with suchtime-sharing light-irradiating and receiving means, if the levelrequired for the detection signal IntD is about the level of the signalD, sampling frequency can be accelerated by making the time interval ofsignals S1 to Sn closer as shown in FIG. 20(B). However, if there is aphase change as the signal D shown in FIG. 20(B), the acceleration maylead to the condition in which the integrator will not be sufficientlyreset at a certain reset time, and the level of remaining precedingsignals may affect the subsequent detection signal IntD. This makesaccurate measurement of the intensity of multiple signals at themultiple irradiating positions difficult, thereby reducing thereliability of measurement results.

As described above, the function required for the detection unit of thebiomedical optical measurement apparatus is to distinguish and detect atransmitted light that corresponds to the light irradiated onto multiplepositions from the light source unit. However, the conventionalbiomedical optical measurement apparatus equipped with a conventionallock-in amplifier using reference signals of multiple frequencies hasvarious unfavorable problems. They include that the instrument should belarge enough to accommodate multiple reference signal generatingcircuits and is not able to cope with changes in the frequency of thereference signal. Also there is a problem common to instruments of atime-sharing light-irradiating and receiving system that a phase changeof the detection signal deteriorates S/N ratio and causes insufficientdistinction.

The first object of this invention, therefore, is to provide abiomedical optical measurement apparatus wherein a lock-in amplifiercomprises a fewer element units. The second object is to provide abiomedical optical measurement apparatus, which is easily able to copewith changes in the frequency. This invention has the third object toprovide a biomedical optical measurement apparatus, which can detect thesignals without deteriorating S/N ratio even when there is a phasedifference between reference signals and signals to be detected. Thisinvention also has an object to provide an biomedical opticalmeasurement apparatus equipped with a time-sharing light irradiating andreceiving means, which properly distinguishes signals to be detectedcontinuously in a time-sharing manner even if there is phase fluctuationin the signals to be detected, and which has an improved reliability inmeasurement. Further, this invention has an object to provide adetection circuit, which can be applied to all types of biomedicaloptical measurement apparatuses.

DISCLOSURE OF THE INVENTION

The biomedical optical measurement apparatus of this invention comprisesa light source means for generating an inspection light containingmultiple lights modulated at different frequencies, a light-receivingmeans for receiving the light generated at the aforementioned lightsource means and passing through an object to be examined and foroutputting electric signals with the intensity corresponding to thereceived inspection light, and a detection means for detecting a signalwith the same frequency of the reference signal from the output fromsaid light-receiving means, wherein said detection means comprises ananalog-digital conversion means for outputting digitized data byconverting an input signal to a digital signal, a storage means forstoring digitized data of multiple reference signals, a digitalmultiplication means for multiplying digitized data of input signalsoutputted from said analog-digital converting means by the digitizeddata of the reference signals read out from said storage means and foroutputting the product of multiplication, and a digital band-limitationmeans for taking out DC data from the output from said digitalmultiplication means (Claim 1).

According to this biomedical optical measurement apparatus, by storingdigitized data of multiple signals in the storage means, it becomesunnecessary to provide reference signal generating circuits in a numberequal to the number of frequencies of the signal to be detected. Also,it can easily cope with changes in the frequency of the signal to bedetected by rewriting data in the storage means and storing digitizeddata of reference signals with new frequencies.

In the aforementioned biomedical optical measurement apparatus of thisinvention, said digital multiplication means and said digitalband-limitation means are composed by a digital signal processor (Claim2). Use of the digital signal processor can significantly reduce thescale of the circuit.

The biomedical optical measurement apparatus of this invention furthercomprises a delaying means for delaying digitized data of the referencesignals (Claim 3). The delaying means is to correct a phase difference,if any, between the signal to be detected and the reference signal.Correction of the phase difference can prevent a decline of the level ofthe signal to be detected and ensure a sufficiently high S/N ratio.

The biomedical optical measurement apparatus of this invention furthercomprises a function generating means which inputs the digitized data ofsaid reference signal and generates a function that becomes “0” or“close to 0” near the level changing point of the digitized data (Claim4).

Phase difference between the signal to be detected and the referencesignals is generated and changes near the area where the referencesignal level changes from “0” to “1” or from “1” to “0”, namely near thelevel changing point. Therefore, by generating a specific function inaccordance with the reference signal, namely, the function which becomes“0” or “close to 0” near the level changing point of reference signal(for example, trigonometric function, Gaussian function or Windowfunctions, such as Hamming and Hanning window functions), multiplyingthe signal to be detected by said function and applying filteringprocessing to them, the level of detection signals will not change andbecomes relatively stable even if the phase changes.

Further, the biomedical optical measurement apparatus of this inventioncomprises a light source means for generating multiple inspection lightsin a time-sharing manner, a light-receiving means for sequentiallyreceiving the inspection light which is generated at said light sourcemeans and passing through an object to be examined, and a detectionmeans for detecting signals from said light-receiving means and foroutputting them as signals for each of the multiple inspection lights;wherein said detection means further comprises an analog-digitalconversion means for converting analog input signals to digital signalsand for outputting digitized data of the input signals, a clock meansfor generating a timing signal so that said analog-digital convertingmeans can begin analog-digital conversion at a specified samplingtiming, a function generating means for generating functions whichbecome “0” or “close to 0” near the sampling time of said input signals,a digital multiplying means for multiplying digitized data of inputsignals outputted from said analog-digital converting means by thefunction of said function generating means and for outputting theproduct of multiplication (Claim 8).

In detecting multiple inspection lights to be outputted in atime-sharing manner by the time-sharing light irradiating and receivingfunction, this biomedical optical measurement apparatus can detectindividual inspection lights accurately without overlapping of precedingsignals over detected signals.

Further, the biomedical optical measurement apparatus of this invention,which has a aforementioned time-sharing light-irradiating and receivingfunction, comprises an integrating means for adding the output from saiddigital multiplication means posterior the digital multiplication means(Claim 9). By equipping the integrating means, the S/N ratio of thesignals can be improved.

Further, the biomedical optical measurement apparatus of this inventionis equipped with, as a detection means, a digital lock-in amplifiercomprising aforementioned analog-digital conversion mean, digitalmultiplication means and digital band-limiting means, and a time-sharinglight irradiating and receiving means. The time-sharing lightirradiating and receiving means is a means with a function to identifythe measurement location by sequentially irradiating a light from thelight source means (light emitting probe) and receiving it at thelight-receiving means (light-receiving probe). Specifically, it is acontrol means for controlling irradiation of the inspection light fromthe light source means and detection of the light by the detection meansin accordance with timing signal generated at specified intervals in atime-sharing manner (Claim 10). More specifically, said control meanscomprises, as a detection means, an amplifier to output multiple signalssequentially outputted from the light-receiving means as continuoussignals, an analog-digital converting means for performinganalog-digital conversion of the output from said amplifier and acontrol means for controlling said detection means, wherein the samplingtiming in said analog digital conversion means is controlled by thetiming signal from said control means (Claim 11).

In a preferred embodiment, a biomedical optical measurement apparatus ofthe invention comprises, as a time-sharing light-irradiating andreceiving means, aforementioned, analog-digital converting means forperforming analog-digital conversion and outputting digitized data ofthe input signals, a clock means for generating timing signals for saidanalog-digital converting means to perform analog-digital conversion ata specified sampling timing, a function generating means for generatinga function which becomes “0” or “close to 0” near the sampling time ofsaid input signals and a digital multiplying means for multiplyingdigitized data of input signals output from said analog-digitalconversion means by the function from said function generating means,and output the product of the multiplication (Claim 12), and furthercomprises an integrating means for adding output from the digitalmultiplying means posterior the digital multiplying means (Claim 13).

According to this biomedical optical measurement apparatus, byselectively employing either a lock-in amplifier or a time-sharing lightirradiating and receiving means the scale of circuit and the like can bechanged according to individual requirements. Employment of both lock-inamplifier and a time-sharing light irradiating and receiving meansassures confident actions and improves reliability. Employment of bothof them also ensures easier receiving of light at the light-receivingposition closely located from the light source means thereby improvingresolution regarding optical measurement.

Further, this invention provides a detection circuit for a biomedicaloptical measurement apparatus. This detection circuit comprises ananalog-digital converting means for performing analog-digital conversionof input signals and outputting digitized data of the input signals, afunction generator for generating one or more functions to be selectedfrom trigonometric function, Gaussian function, Hamming and Hanningwindow functions, a multiplying means for multiplying output from saidanalog-digital converting means by the function generated from saidfunction generator (Claim 14), and further comprises an adding means forfeeding back the sum (results of addition) from itself and adding thesum to the output from said multiplying means (Claim 15).

This detection circuit can be applied to the biomedical opticalmeasurement apparatus of either lock-in amplifier or time-sharing lightirradiating and receiving system, and can solve the problem that isassociated with phase fluctuations of signals to be detected and commonto both systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the configuration of majorcomponents in the first embodiment of a biomedical optical measurementapparatus according to the present invention;

FIG. 2 is a block diagram of a lock-in amplifier in FIG. 1;

FIG. 3 is a diagram showing an exemplary layout of inspection lightirradiating and light-receiving positions in a biomedical opticalmeasurement apparatus;

FIG. 4 is a graph explaining the frequency characteristics of anantialiasing low-pass filter and the frequencies of input signals;

FIG. 5 is a graph explaining frequency characteristics of a digitallow-pass fitter and signals after locked-in;

FIG. 6 is a block diagram showing the configuration of a lock-inamplifier used in the biomedical optical measurement apparatus accordingto the second embodiment of the present invention.

FIG. 7 is a block diagram showing the configuration of a variant of thelock-in amplifier in FIG. 6.

FIG. 8 is a block diagram showing the configuration of another variantof the lock-in amplifier in FIG. 6.

FIG. 9 is a block diagram showing the configuration of a variant of thelock-in amplifier in FIG. 7.

FIG. 10 is a block diagram showing the configuration of a variant of thelock-in amplifier in FIG. 9.

FIG. 11 is a block diagram showing the configuration of an improvedlock-in amplifier in FIG. 6;

FIG. 12 is a block diagram showing the configuration of a furtherimproved lock-in amplifier in FIG. 6;

FIG. 13 is a diagram representing an example of a biomedical opticalmeasurement apparatus, which can cope with phase changes at acceleratedsampling frequency;

FIG. 14 is a block diagram showing a lock-in amplifier of a conventionalbiomedical optical measurement apparatus;

FIG. 15 is a block diagram showing the detailed configuration of thelock-in amplifier in FIG. 14;

FIG. 16 is a timing chart showing signal waveforms to explain theactions of the lock-in amplifier in FIG. 15;

FIG. 17 is a timing chart showing signal waveforms to explain theactions of the lock-in amplifier in FIG. 14, in cases that the signal tobe detected have phase difference from that of reference signal and thatthe phase difference changes;

FIG. 18 is a drawing showing a prior art biomedical optical measurementapparatus equipped with a time-sharing light irradiating and receivingmeans.

FIG. 19 is a drawing showing another biomedical optical measurementapparatus to which improvements are given to the biomedical opticalmeasurement apparatus in FIG. 18 for increasing the S/N ratio.

FIG. 20 is a drawing showing an example in which the sampling frequencyin a biomedical optical measurement apparatus in FIG. 19 is accelerated.

PREFERRED EMBODIMENT OF THE INVENTION

Embodiments of this invention will be explained hereinafter with thereference of the attached drawings.

FIG. 1 is a block diagram illustrating the configuration of a biomedicaloptical measurement apparatus according to one embodiment of the presentinvention, and FIG. 2 is a block diagram showing the configuration of alock-in amplifier equipped in the measurement apparatus. As shown inthese figures, the biomedical optical measurement apparatus comprises alight source unit 11, which generates an inspection light to beirradiated onto an object to be examined 20, a light-receiving unit 12,which receives the light passing through the test object or reflectingnear the surface of the object 20 (transmitted light, collectively) andoutputs electric signals with intensify corresponding to the receivedlight, an lock-in amplifier 10, which detects the light received at thelight-receiving unit 12 in accordance with its frequency, an arithmeticoperation unit 30, which input the outputted signals from the lock-inamplifier 10, calculates biomedical information (including hemoglobinconcentration) at the inspection light irradiating positions anddisplays the calculation results, and a control unit 35, which controlsthe actions of the light source 11, the light-receiving unit 12, thelock-in amplifier 10 and the operation unit 30. Although the arithmeticoperation unit 30 and the control unit 35 are separately shown in FIG.1, both arithmetic operation unit 30 and control unit 35 can be built ona personal computer equipped with an input/output devices such asincluding display and keyboard.

The light source unit 11 comprises multiple light sources, at each ofwhich the inspection light is modulated by different frequencies.Although a light with a single wavelength can be used as an inspectionlight, two lights with different wavelengths, for example 780 nm and 830nm, are usually employed. If the lights with wavelength of 780 nm and830 nm are modulated with 8 different frequencies, for example, theinspection light will comprise lights modulated at 16 differentfrequencies.

Sixteen different inspection lights from the light source unit 11 areguided, through optic fibers, for example, to specified inspectionpositions of the object 20, and irradiated from the surface of theobject to the interior of the object, wherein the lights of twodifferent wavelengths are guided as one set of light to one optic fiber.The light passing through the object 20 is guided by the optic fiberplaced near the optic fibers for irradiation and received at thelight-receiving unit(s) 12. The light-receiving unit 12 outputs anelectric signal with an intensity corresponding to that of the receivedinspection light.

FIG. 3 shows the layout of the light irradiating position 31 and thelight-receiving position 32. In the example shown in FIG. 3(A), each ofthese two light-receiving positions 321 and 322 is surrounded by 4 tipsof optic fiber for irradiating light (irradiated positions) 311 to 314and 315 to 318, respectively. In this layout, because thelight-receiving position 32 receives lights with 2 different wavelengthsfrom 4 directions, this position receives 4×2=8 signals. The followingexplanation concerns the instrument equipped with two light-receivingunits 12. However, the number of the light-receiving units 12 needs notbe limited to two, and can be varied in accordance with the object. Forexample, in order to inspect a relatively large area, irradiationpositions (shown with ●) 31 and the light-receiving positions (shownwith ◯) 32 are laid alternately on a matrix. Also in this case, onelight-receiving position receives lights with 2 different wavelengthsfrom 2 or 4 directions, namely a composite light which is modulated atmaximum 16 different frequencies.

The lock-in amplifier unit 10 receives a synthetic signal made ofmultiple signals with different frequencies as an input signal, anddetects them as individual signals separated by each frequency. Thelock-in amplifier unit 10 is equipped with antialiasing low-pass filters(ALPF) 2, A/D converters 3, a reference signal memory 5, a digitallock-in circuit 8 and a buffer memory 9. The input signals are signalswith an intensity corresponding to that of light as mentionedpreviously, so that they contain multiple signals with, for example, 8different frequencies. They are amplified by the amplifier, which is notshown in the figure. Two sets of an antialiasing low-pass filter 2 andA/D converter 3 are installed in correspondence to two input electricsignals.

The antialiasing low-pass filters 2 attenuate the signals having afrequency higher than that of a reference signal contained in the inputsignal, particularly the signals that are generated by noise and Nyquistfrequency, and output them into the A/D converters. FIG. 4 shows arelationship between frequency characteristics of the antialiasinglow-pass filter 2 and frequency of the input signal. In FIG. 4, thewaveform 41 shows the frequency characteristics of the antialiasinglow-pass filter.

If the frequencies of n+1 signals contained in the input signal areassumed as fs, fs+fp, fs+2fp, . . . fe (=fs+nxfp), the cut off frequencyfc of the antialiasing low-pass filter 2 is higher than fe (fc>fe).Also, when the attenuation-band frequency of the antialiasing low-passfilter 2 and Nyquist frequency are defined as fa′ and f, respectively,the frequency of the signal to be detected is expressed as f−(fa′−f)>fe.

The A/D converters 3 convert analog signals outputted from theantialiasing low-pass filter 2 to digital signals and output them. Thebuffer memory 9 temporarily stores the data outputted from two sets ofA/D converters 3 and outputs them into the digital lock-in circuit 8.

The digital lock-in circuit 8 is equipped with a multiplier 4, alow-pass filter 6 and a control unit (not shown in the figure). Thedigital multiplier 4 sequentially multiplies digitized data of the inputsignals outputted from the A/D converters 3 by digitized data of thereference data readout sequentially from the reference signal memory 5,and outputs the multiplied signals into the digital low-pass filter 6.

The reference signal memory 5 pre-stores digitized data of multiplereference signals R1 to Rn, for example, digitized data of the referencesignals with 16 different frequencies which correspond to those of theinput signal. If the frequencies to be used for modulation are changedat the light source unit 11, the data in the reference signal memory 5are re-written and digitized data of the reference signals with newfrequencies are stored.

The digital low-pass filter 6 takes out the DC component from themultiplied signals outputted from the digital multiplier 4, and outputsit as an output signal 7 in the operation unit 30. FIG. 5 shows arelationship between the frequency characteristics of the digitallow-pass filter 6 and the signals after locked-in. In FIG. 5, thewaveform 51 shows the frequency characteristics of the digital low-passfilter 6, while the signals 52 and 53 show the waveform after locked-inby the digital multiplier 4. When the digital low-pass filter 6 takes DCdata out from the signals 52 and 53 locked-in the digital multiplier 4,since an attenuation-band frequency fa is set for the digital low-passfilter 6 as shown in FIG. 5, the signal 53 (signal other than the signal52) after locked-in by digital multiplier 4 has a center frequency fpand the frequency pitch between signal 52 and the other signal 53 afterlock-in becomes fp. The relationship between the attenuation-bandfrequency fa of the digital low-pass filter and the center frequency fpof the other signal 53 after lock-in satisfies fp≧2fa. All other signalsto be detected should mutually have the frequency pitch of fp. This isto obtain a necessary amount of attenuation of noise and other signalsfor a signal to be locked-in.

The digital lock-in circuit 8 (digital multiplier 4, digital low-passfilter 6 and the like) may consist of electronic components such asdigital signal processor (DSP)).

Actions of the lock-in amplifier 10 having such configuration areexplained. First, the control circuit in the digital lock-in circuit 8transmits a control signal 8 a to the buffer memory 9, reads out eitherof the data witch are outputted from 2 sets of A/D converters 3 andstored in the buffer memory 9. It also transmits a control signal 8 b tothe reference signal memory 5 and sequentially reads out digitized dataof reference signals stored in the reference signal memory 5. Thedigital multiplier 4 sequentially multiplies the data read out from thebuffer memory 9 by digital data of reference signals sequentially readout from the reference signal memory 5 and outputs the results ofmultiplication. The digital low-pass filter 6 takes out the DC data fromthe output of the digital multiplier 4, and outputs them as an outputsignal.

According to this embodiment of this invention, by storing digitizeddata of multiple reference signals in the reference signal memory 5 itbecomes unnecessary to provide the reference signal generating circuitsin a number equal to the number of frequencies to be detected as in theconventional embodiment. One of the examples is that one digital lock-incircuit can serve as 16 analog lock-in amplifiers required forconventional configurations. Moreover, as digitized reference signalswith new frequencies can be stored only by re-writing the data stored inthe reference signal memory 5, it becomes easier to deal with changes infrequencies.

This embodiment of the invention has been explained with the case inwhich a pair of lights each having light different wavelength ismodulated with 8 different frequencies. However, this invention is notlimited to this embodiment, and can be applied to the case in which twoor more lights with one or more different wavelengths are modulated bytow or more frequencies. The light-receiving unit 12 has been describedwith the case in which two signals are to be detected, but the number ofsignals to be detected is not limited to two.

Further, while one digital lock-in circuit 8 sequentially processesmultiple reference signals with different frequencies in thisembodiment, it is possible to install one processing circuit for eachmodulation frequency. Such embodiments are explained hereinafter withreference to FIGS. 6 to 10.

FIG. 6 shows a block diagram of a lock-in amplifier to be used in thebiomedical optical measurement apparatus according to the secondembodiment of this invention. Also in this second embodiment, aninspection light 60 passing through the object is received by alight-receiving element (diode) 61, converted photoelectrically andoutputted as a signal with an intensity corresponding to that of thelight into the amplifier 62, as in the embodiment shown in FIGS. 1 and2. In this embodiment, the signals amplified by the amplifier 62 areinputted in digital lock-in circuits 601, 602 . . . which are installedat every frequency component. The input signal is a synthesized signalmade of multiple signals with different frequencies. While only digitalprocessing circuits 601 and 602 in 2 systems are shown in the figures,the digital circuits of similar configuration can be installed in anumber equal to the number of frequencies (n) of the signals to bedetected. As the configuration of every digital lock-in circulation 601is similar except for the reference signal to be used, one digitallock-in circuit 601 will be explained.

The digital lock-in circuit 601 constitutes a digital lock-in amplifierhaving an A/D converter 631, two digital multipliers 641 and 651 and anadder 661. Posterior the adder, there is provided a latch circuit 681for latching output signals from each digital lock-in circuit 601 andinputting them into the operation unit 69.

The A/D converter 631 converts the output from the amplifier 62 andoutputs it to the digital multiplier 641. The digital multiplier 641multiplies the output from the A/D converter 631 by the reference signalF1, and outputs the result of the multiplication into the followingdigital multiplier 651. Specifically, the digital multiplier 641multiplies input signals by +1 or −1 according to the frequency of thereference signal F1. Digitized data of the reference signal to be usedin the digital multiplier 641 is stored, as in the embodimentillustrated in FIG. 1, in the reference signal memory not illustrated inthe figure.

The digital multiplier 651 multiplies the output from the digitalmultiplier 641 by a low-pass filter coefficient stored in thecoefficient ROM 671, and outputs the result of the multiplication intothe following digital adder 661. The digital adder 661 sequentially addsthe output from the digital multiplier 651 and the sum fedback from theadder itself, processes it to take out a DC component and outputs intothe latch circuit 681.

Filtering processing by this digital multiplier 651 and the digitaladder 661 is similar to the processing by the digital low-pass filter 6in the embodiment shown in FIG. 1 (FIG. 2), with the frequencycharacteristics being similar to what is shown in FIG. 5.

The latch circuit 681 latches signals which are subjected to filteringprocessing by the digital multiplier 651 and the digital adder 661, andoutputs them in the operation unit (PC) 69.

FIG. 7 is a block diagram showing a variant of the lock-in amplifiershown in FIG. 6. Since components of the lock-in amplifier in FIG. 7with the same configuration as those in FIG. 6 are marked with the samesymbols, explanation thereof is excluded. This lock-in amplifier isdifferent from that in FIG. 6 in that the digital multipliers 641, 642,651 and 652 and the digital adders 661 and 662 in FIG. 6 are replaced bythe digital signal processors (DSP) 71 and 72.

FIG. 8 is a block diagram showing another variant of the lock-inamplifier shown in FIG. 6. Since components of the lock-in amplifier inFIG. 8 with the same configuration as those in FIG. 6 are marked withthe same symbols, explanation is thereof excluded. This lock-inamplifier is different from that in FIG. 8 in that the analog/digitalconversion is performed by one A/D converter 63. Specifically, in thelock-in amplifier in FIG. 6 the output from the amplifier 62 issubjected to analog/digital conversion by the A/D converters 631 and 632installed prior to each digital lock-in circuit 601 and 602,respectively, whereas in the lock-in amplifier in FIG. 8 the output fromthe amplifier 62 is subjected to analog/digital conversion by one A/Dconverter 63 and the output from the A/D converter 63 is then inputtedinto each digital lock-in circuit 601 and 602, which comprise thedigital multipliers 641, 642, 651 and 652, and the digital adders 661and 662.

FIG. 9 is a block diagram for another variant of the lock-in amplifiershown in FIG. 7. Since components of the lock-in amplifier in FIG. 9having the same configuration as those in FIG. 7 are marked with thesame symbols, explanation thereof is excluded. The lock-in amplifiershown in FIG. 9 is different from that in FIG. 7 in that a single A/Dconverter 63 is used for analog-digital conversion in the lock-inamplifier in FIG. 9.

FIG. 10 is a block diagram for another variant of the lock-in amplifiershown in FIG. 9. Since components of the lock-in amplifier in FIG. 10having the same configuration as those in FIG. 9 are marked with thesame symbols, explanation is thereof excluded. The lock-in amplifiershown in FIG. 10 is different from that in FIG. 9 in that the lock-inamplifier in FIG. 10 uses the digital signal processor (DAP) 70 fordigital signal processing, and the results are latched in multiple latchcircuits 681 to 68 n. This configuration (variation) is similar to thevariant of the embodiment in FIG. 1, in which a digital lock-in circuit8 (digital multiplier 4, digital low-pass filter 6, and like) isreplaced by a digital signal processor (DSP).

As mentioned above, there can be various configurations of the lock-inamplifier to be employed in the biomedical optical measurement apparatusof this invention as shown in FIGS. 6 to 10. It is desirable to employoptimal circuits in view of the purpose of use and the scale of circuit.

Next, as another embodiment of this invention, there will be explainedconfiguration of a lock-in amplifier having means for correcting phasedifference when the signal to be detected has phase difference from thereference signal. The means for correcting such phase difference can beapplied to all lock-in amplifiers illustrated in FIGS. 6 to 11 mentionedabove. An example in which the correction means is applied to thelock-in amplifier in FIG. 9 is shown in FIG. 11. Components of thelock-in amplifier in FIG. 11 having the same configuration as those thatin FIG. 9 are marked with the same symbols and explanation thereof isexcluded.

The lock-in amplifier in FIG. 11 is different from that in FIG. 9 inthat reference signals F1 and F2 are supplied to the digital signalprocessors (DSP) 71 and 72 through the delay circuits (DELAY) 81 and 82in the lock-in amplifiers in FIG. 11. By installing these delay circuits81 and 82, the reference signals F1 and F2 can be supplied to thedigital signal processors (DSP) 71 and 72 after correcting phasedifference if the signals to be detected have phase difference from thatof the reference signal Fn. Delaying reference signals in accordancewith phase difference can prevent the decline in the level of detectionsignal by the phase difference as shown in FIG. 17(A) and ensures asufficiently large S/N ratio.

Next, as yet another embodiment of this invention, the configuration ofa lock-in amplifier having a means for preventing declining of signaldue to changes in phase difference between signals to be detected andreference signals. Such means can be applied to all lock-in amplifiersshown in FIGS. 6 to 11 mentioned above. An example of such means appliedto the lock-in amplifier of FIG. 11 is shown in FIG. 12. Components ofthe lock-in amplifier in FIG. 12 having the same configuration as thosein FIG. 11 are marked with the same symbols and explanation thereof isexcluded.

As illustrated, the lock-in amplifiers of this embodiment is equippedwith function generating circuits 91 and 92, which generate specifiedfunction waveforms in accordance with reference signals Fn (F1, F2 . . .) to be supplied to the digital signal processors (DSP) 71 and 72through the delay circuits (DELAY) 81 and 82. In order to obtain asignal which certainly synchronize with reference signal Fn bymultiplying the signal to be detected by the function, the function Mnshould have a function waveform which becomes “0” or “close to 0” nearthe level changing point of the reference signal Fn. These functionsinclude trigonometric function, Gaussian function or Window Function,such as Hamming or Hanning window functions.

The relationship between the reference signal Fn, function Mn and asignal to be detected AMP5 is shown in FIG. 12(B). As illustrated in thefigure, phase difference between the signal to be detected AMP6 and thereference signal Fn generally changes in the area where the level of thereference signal Fn changes from “0” to “1” or from “1”, to “0”, or nearthe level changing point. Accordingly, the function Mn, whose functionwaveform becomes “0” or “close to 0” near the level changing point ofthe reference signal Fn is generated in accordance with the referencesignal Fn, and the signal to be detected AMP5 is multiplied by thefunction to produce a multiplication waveform DSP5 using digital signalprocessors 71 and 72. Then this multiplication waveform DSP5 issubjected to filtering processing to obtain a detection signal LPF5. Bythis, the level of detection signal LPF5 will not change and becomesrelatively stable, even if the phase of the signal AMP5 changes as awaveform shown in FIG. 12(B). Delay circuits 81 and 82 shown in FIG.12(A) can be excluded when no certain phase difference exists betweensignals to be detected and reference signals.

The embodiments and variants of the lock-in amplifier unit in thebiomedical optical measurement apparatus equipped with a lock-inamplifier have been explained above. According to this biomedicaloptical measurement apparatus, by constructing a lock-in amplifier witha digital circuit and by equipping a reference signal memory whichstores multiple reference signals with different frequencies asdigitized data, the installation of reference signal generating circuitsin a number equal to that of frequencies of the signals to be detectedbecomes unnecessary and the data can be rewritten easily when thefrequencies are changed. Moreover, the installation of a delay circuitor function generating circuit at the reference signal input side of thelock-in amplifier prevents decline of signals and ensures stablemeasurement even if there occurs a phase difference between a referencesignal and a signal to be detected and the phase difference changes.

The biomedical optical measurement apparatus in these embodiments can beapplied to the biomedical optical measurement apparatus equipped with,for example, conventional time-sharing light irradiating and receivingfunction as shown in FIG. 18 or 19. While a digital lock-in amplifierunit having the same configuration as those shown in FIG. 1 mentionedabove or FIGS. 6 to 12 is installed, in addition to the digital lock-inamplifier unit 10, the measurement apparatus is equipped with, as adetection means, the amplifier 162 which sequentially outputs multiplesignals outputted from the light-receiving element 161 as continuoussignals, and the analog digital converter 163, which performsanalog/digital conversion of the output from the amplifier 162.Irradiation of an inspection light from the light source unit isperformed in time-sharing manner in accordance with a timing signal fromthe control unit 35 (FIG. 1), and the sampling timing in theanalog-digital converter 163 is controlled so as to synchronize withthis timing signal.

Next, another embodiment of this invention is explained. This embodimentis applied to the biomedical optical measurement apparatus, which isequipped with a time-sharing light irradiating and receiving meansinstead of, or in addition to, the aforementioned lock-in amplifier. Thetime-sharing light irradiating and receiving means has a function ofsequentially irradiating light from the light source unit (lightemitting probe), receiving the light at the light-receiving unit(light-receiving probe) to identify the measurement position. Namely,the biomedical optical measurement apparatus equipped with atime-sharing light irradiating and receiving means sequentiallyirradiates light from each light source at the light source unit in atime-sharing manner, and detects only signals with a specific timingfrom the lights detected at the light-receiving position, whereas thebiomedical optical measurement apparatus in FIG. 1 continuouslyirradiate the light with multiple frequencies from each light source atthe light source unit 11, and detects the light with specified frequencyfrom the lights with multiple frequencies detected at thelight-receiving position, by using a lock-in amplifier.

An embodiment of the biomedical optical measurement apparatus equippedwith a time-sharing light irradiating and receiving means is shown inFIG. 13. This biomedical optical measurement apparatus is equipped withthe light source unit 131, which sequentially generates multipleinspection lights to be irradiated onto multiple positions of an objectto be examined 130 in a time-sharing manner, the light-receiving unit132, which receives light passing through the object 130 and outputselectric signals with an intensity corresponding to that of light,time-sharing detection unit 133, which detects the light received at thelight-receiving unit 132, the arithmetic operation unit 134, which inputsignals outputted from the time-shared detection unit 133, calculatesbiomedical information (for example, hemoglobin concentration and like.)at the inspection light irradiation position and displays thecalculation results, and the control unit 135, which controls actions atthe light source unit 131, the light-receiving unit 132 and thetime-sharing detection unit 133. Further, while the operation unit 134and the control unit 135 are shown separately in the embodimentillustrated in the figure, they can be constructed on a PC equipped withI/O devices, such as display and keyboard, as in the biomedical opticalmeasurement apparatus shown in FIG. 1.

The light source unit 131 and the light-receiving unit 132 areconfigured, though simplified in the Figure, as illustrated in FIG. 3for example, so as to irradiate the inspection light from multipleirradiation positions onto the surface of an object to be examined andreceive the light (inspection light) at multiple light-receivingpositions laid out on the designated positions associated with theirradiation positions. The light source unit 131 irradiates a light witha specified frequency on different irradiation positions at certain timeintervals by using a clock signal generated at the clock signalgenerator of the control unit 135. The light-receiving unit 132comprises multiple light-receiving elements or optic fibers each end ofwhich is connected with a light-receiving element. The inspection light160 received by each light-receiving element is outputted into the sameamplifier 162.

The time-sharing detection unit 133 is equipped with the amplifier 162,an A/D converter 163 which performs analog/digital conversion of thesignals amplified by the amplifier 162, a digital multiplier 165 formultiplying output from the A/D converter 163 by a specified function, afunction memory 164, which stores functions to be used by the digitalmultiplier 165, a digital adder 167 which integrates output from thedigital multiplier 165, and a latch circuit 168 which latches outputfrom the digital adder 167.

Also in this biomedical optical measurement apparatus signals S1 to S5with corresponding intensity to that of light and outputted from thelight-receiving element 161 are amplified by the amplifier 162 andinputted as a signal D into the A/D converter 163, as in the biomedicaloptical measurement apparatus referred to in FIG. 18. The A/D converter163 performs A/D conversion of the output from the amplifier 162 at asampling time synchronized with a clock signal CLOCK, and outputs theminto the digital multiplier 165. The function memory 164 contains afunction, which becomes “0” or “close to 0” near the sampling timing,for example, trigonometric function, Gaussian function or windowfunctions, such as Hamming and Hanning functions. These functions aresimilar to those generated by the function generating circuits 91 and91, which are employed in the lock-in amplifier in FIG. 12. Themultiplier 165 reads the aforementioned specific function from thefunction memory 164, multiplies the output from the A/D converter 163 bythe function and outputs the product of the multiplication into thefollowing digital adder 167.

The digital adder 167 sequentially adds the output from the digitalmultiplier 165 and the sum fedback from itself, performs integrationprocessing, and outputs the integrated signals into the latch circuit168. Processing by the digital adder 167 is reset at the timesynchronized with the clock signal CLOCK. The latch circuit 168 latchesthe signals integrated by the digital adder 167 with the sampling timing(CLOCK), and outputs them into the operation unit (PC) 134.

According to the biomedical optical measurement apparatus of thisembodiment, by multiplying the output from the A/D converter 163 by thefunction, which becomes “0” or “close to 0” near the sampling timing,the level of detection signal IntD becomes unchanged even the phasechanges as shown in the waveform D referred to in FIG. 19(B), therebypreventing the error attributable to the phase change.

As an embodiment of this invention, the improvement to the biomedicaloptical measurement apparatus employing a time-sharing light irradiatingand receiving means has been described with reference to FIG. 13. Suchimprovement can be applied not only to the biomedical opticalmeasurement apparatus equipped with a time-sharing light irradiating andreceiving means but also to the biomedical optical measurement apparatusequipped with both a lock-in amplifier and a time-sharing lightirradiating and receiving means. Particularly, the employment of thelock-in amplifier and the time-sharing light irradiating and receivingmeans as described above ensures confident actions and improvesreliability. Moreover, the employment of both can make it easier toreceive the inspection light at the light source and light-receivingunits placed closely, thereby improves resolution regarding opticalmeasurement.

INDUSTRIAL APPLICABILITY

According to the biomedical optical measurement apparatus of thisinvention, by storing digitized data of multiple reference signals in astoring means, the provision of the reference signal generating circuitsof a number equal to that of frequencies of signals to be detected canbe unnecessary, and the number of units required in the configuration ofthe lock-in amplifier can be reduced. Moreover, according to thebiomedical optical measurement apparatus of this invention, changes infrequency can be easily coped with by only re-writing the data of thestoring means and storing digitized reference signals with newfrequencies. Moreover, according to the biomedical optical measurementapparatus of this invention, signals can be detected withoutdeteriorating S/N ratio even when there is phase difference between thesignals to be detected and reference signals.

1. A biomedical optical measurement apparatus comprising: a light sourcemeans for generating an inspection light containing multiple lightsmodulated at a given number of different frequencies, a light-receivingmeans for receiving the light generated at said light source means andpassed through an object to be examined and for outputting synthesizedsignals made of a given number of electric signals each having adifferent frequency and an intensity corresponding to the receivedlight, and a detection means for detecting a signal with the samefrequency as a frequency of a reference signal having a frequencycorresponding to frequencies of modulated multiple lights in thesynthesized signals, wherein said detection means comprises: ananalog-digital conversion means for outputting digitized synthesizedsignal data by converting said synthesized signals having differentfrequencies to a digital signal, a storage means for storing digitizeddata of a number of reference signals, where the number of referencesignals is equal to the number of the synthesized signals output fromthe light-receiving means, a delaying means for delaying said referencesignals data read out from the storage means based on phase differencesbetween said synthesized signals data output from said analog-digitalconversion means and said reference signals data read out from thestorage means, a digital multiplication means for multiplying saidsynthesized signals data output from said analog-digital conversionmeans by said reference signals data delayed by the delaying means andfor outputting the product of multiplication, and a digitalband-limitation means for taking out DC data from the output from saiddigital multiplication means.
 2. The biomedical optical measurementapparatus of claim 1, wherein said digital multiplication means and saiddigital band limitation means are composed by a digital signalprocessor.
 3. The biomedical optical measurement apparatus of claim 1,further comprising a function generating means for inputting thedigitized data of said reference signals and for generating a functionthat becomes “0 ” or “close to 0 ” near a level changing point of thedigitized data.
 4. The biomedical optical measurement apparatus of claim1, wherein a digital signal processor including said digital multiplyingmeans and said digital band-limitation means is provided for eachmodulation frequency.
 5. The biomedical optical measurement apparatus ofclaim 4, wherein the digital multiplying means further comprises: afirst digital multiplication means for multiplying digitized data ofinput signals outputted from said analog-digital conversion means by thedigitized data of the reference signals read out from said storage meansand for outputting the product of multiplication, and a second digitalmultiplication means for multiplying the output from said first digitalmultiplication means by a low-pass filter coefficient and for outputtingthe product of multiplication.
 6. The biomedical optical measurementapparatus of claim 1, wherein said digital band-limitation means has anattenuation-band frequency fa satisfying fp≧2fa when a frequencyinterval (pitch) of signals to be detected is fp.
 7. The biomedicaloptical measurement apparatus of claim 1, further comprising a controlmeans for controlling said light source means, said light-receivingmeans and said detection means, wherein said control means generatestiming signals with a predetermined interval and controls irradiation ofthe inspection light from the light source means and signal detection bythe detection means in a time-sharing manner according to the timingsignal.
 8. The biomedical optical measurement apparatus of claim 1,further comprising an amplifier for outputting multiple signalssequentially outputted from said light-receiving means as a continuoussignal, and a control means for controlling the detection means, whereina sampling time at the analog-digital conversion means is controlled bya timing signal outputted from said control means.
 9. The biomedicaloptical measurement apparatus of claim 1, wherein the detection meansfurther comprises: a clock means for generating timing signals for saidanalog-digital conversion means to perform analog-digital conversion ata specified sampling timing, a function generating means for generatinga function which becomes “0 ” or “close to 0 ” near the sampling time ofsaid input signals, and a digital multiplying means for multiplying thedigitized data output from said analog-digital conversion means by thefunction from said function generating means, and outputting the productof the multiplication.
 10. The biomedical optical measurement apparatusof claim 9, further comprising an integrating means for adding theoutput from said digital multiplying means posterior the digitalmultiplying means.
 11. A biomedical optical measurement apparatuscomprising: a light source means for generating multiple inspectionlights modulated at different frequencies in a time-sharing manner, alight-receiving means for sequentially receiving the inspection lightgenerated at said light source means and passed through an object to beexamined and for outputting synthesized signals made of electric signalshaving different frequencies with an intensity corresponding to thereceived inspection light, and a detection means for detecting signalswith the same frequency corresponding to frequencies of modulatedmultiple lights in the synthesized signals; wherein said detection meansfurther comprises: an analog-digital conversion means for outputtingdigitized synthesized signals data by converting said synthesizedsignals having different frequencies to a digital signal, a clock meansfor generating a timing signal so that said analog-digital convertingmeans can begin analog-digital conversion at a specified samplingtiming, a function generating means for generating functions whichbecome “0 ” or “close to 0 ” near the sampling time of said synthesizedsignals, a delaying means for delaying said functions based on phasedifferences between said synthesized signals data output from saidanalog-digital conversion means and said timing signal of said clockmeans, and a digital multiplying means for multiplying digitizedsynthesized signals outputted from said analog-digital converting meansby the function of said function generating means and for outputting theproduct of multiplication.
 12. The biomedical optical measurementapparatus of claim 11, further comprising an integrating means foradding the output from said digital multiplication means posterior thedigital multiplication means.
 13. A detection circuit for a biomedicaloptical measurement apparatus comprising; an analog-digital convertingmeans for performing analog-digital conversion of input signals and foroutputting digitized data of the input signal, a function generator forgenerating one or more functions to be selected from trigonometricfunction, Gaussian function, Hamming and Hanning window functions, adelaying means for delaying said functions based on phase differencesbetween said digitized data output from said analog-digital conversionmeans and said functions generated from said function generator, and amultiplying means for multiplying output from said analog-digitalconverting means by the function generated from said function generator.14. The detection circuit of claim 13, further comprising, posteriorsaid multiplying means, adding means for feeding back the sum (resultsof addition) from itself and adding to the output from said multiplyingmeans.